💡 Add a `get` method

[pjechris]

Summary

Today we have find methods which returns a successful observer only if the value is already stored.

Idea would be to add a get counterpart which would always suceeds. This would allow to declare an observer even if the value is not yet present.

To be consistent find(named:) would be renamed get(named:) as aliases never fail

Basic Example

identityMap.find(Foo.self, id: 1) // returns nil because value is not stored yet
identityMap.get(Foo.self, id: 1) // returns an Observer even if value is not stored. Might never receive any value if Foo(id:1) is never stored

identityMap.store(Foo(id: 1, title: "hello world")) // observer is notified

Unresolved questions

Implementing such feature would require refactoring on how observers are handled currently: for now observer is tightly tied with the presence of the value in IdentityMap.

We would need a way of declaring such an observer even when value is not stored yet.